Method of forming insulating films, capacitances, and semiconductor devices

ABSTRACT

Insulating metal oxide or nitride films are deposited by RF magnetron sputtering. During sputtering, the atmospheric gas comprises an oxygen or nitride compound gas and an inert gas. The proportion of the inert gas is decreased to 25 atom % or lower. By this sputtering condition, adverse effects caused by the inert gas is suppressed so that the quality of the insulating film is substantially improved.

This is a continuation of Ser. No. 08/041,520, filed Mar. 30, 1993, nowabandoned, which itself was a continuation of Ser. No. 07/729,533, filedJul. 15, 1991, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming insulating films ingeneral. More particularly, it relates to such a method of sputteringsuitable for forming excellent dielectric films suitable for use incapacitances.

In the recent years, dielectric (insulating) films deposited by CVD havebeen utilized to form capacitances for use in integrated semiconductordevices. The employment of CVD makes it possible to deposit dielectricfilms at low temperatures up to 450° C. so that inexpensive substratessuch as soda lime glass or borosilicate glass substrates can be used.Similar low temperature deposition can be accomplished also by plasmaCVD and sputtering in an atmosphere comprising an inert gas such asargon at a density of 100% to 80%. The use of argon has been known toincrease the sputtering yield.

In accordance with experiments of the inventor, it has been found thatthe number of the interface states occurring between the dielectric filmand the underlying electrical active region seriously depends upon theargon density of the sputtering atmosphere. A conspicuous example is thecase of dielectric films made of tantalum oxide. In this case, manyclusters of tantalum atoms of 5 to 50 Å diameter are formed in the oxidefilm due to stability of metal tantalum. It has been also found that theargon density significantly influences the difference in flat bandvoltage from the ideal value which indicates the degradation of the filmand reflects the state number of fixed charge and the clusters.

There are other attempts to form dielectric films by the use ofphoto-CVD. In this case, the underlying surface is less damaged and thedensity of interface states is as low as 2×10¹⁰ eV⁻¹ cm⁻². On the otherhand, the deposition of photo-CVD takes much time to complete due tovery slow deposition speed so as not to be utilized for massproduction.Furthermore, the long-term reliability is not sure because ofhot-electron effect resulting from hydrogen utilized during deposition.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of forminghigh quality insulating films by deposition at low temperatures suitablefor use in capacitances.

It is another object of the present invention to provide a method offorming high quality insulating films having high reliability.

It is a further object of the present invention to provide a method offorming a semiconductor device having high reliability.

Additional objects, advantages and novel features of the presentinvention will be set forth in the description which follows, and inpart will become apparent to those skilled in the art upon examinationof the following or may be learned by practice of the present invention.The object and advantages of the invention may be realized and attainedby means of the instrumentalities and combinations particularly pointedout in the appended claims.

To achieve the foregoing and other object, and in accordance with thepresent invention, as embodied and broadly described herein, adielectric material or an insulating material is sputtered on asubstrate in a particularly appropriate atmosphere. Unlike conventionalprocess, the atmosphere is characterized in that no or small proportionof an inert gas, typically argon, is utilized. The inventors havepresumed that the disadvantages of argon atoms include stoichiometricdisturbance in the product of sputtering and damage or defects caused bycollision of argon ions or argon atoms with the dielectric filmresulting in formation of fixed charge.

In the case of sputtering of a metal oxide such as tantalum oxide,titanium oxide or other suitable oxide dielectric materials and bariumtitanate, lead titanate or similar ferro-electric materials, the insideof a sputtering apparatus is filled with an oxidizing gas containing aninert gas at 25 vol. % or less, e.g. a mixture of oxygen (100% to 75% involume) and argon (0% to 25% in volume). Other suitable oxidizing gasesinclude N₂ O and O₃. Particularly, in the case of O₂ or O₃, unnecessaryatoms are not introduced into the oxide film resulting in few pinholes,little damage to dielectric properties and decreased dispersion indielectric strength. O₃ tends to be decomposed to yield oxygen radicalswhich enhance progress of the deposition. Usually, a bulk of a desiredone of these oxides is used as the target of the sputtering. A simplemetal such as tantalum can be also used as the target by suitablyselecting the sputtering condition as explained in the followingdetailed description.

In the case of sputtering of nitrides, e.g. insulating nitrides such assilicon nitride and aluminum nitride, or resistive nitrides such astantalum nitride, titanium nitride or other suitable nitride, the insideof a sputtering apparatus is filled with a nitride compound gascontaining an inert gas at 50 vol. % or less, preferably 25 vol. % orless, e.g. a mixture of nitrogen (100 vol. % to 75 vol. %) and argon (0vol. % to 25 vol. %). Other suitable nitride compound gases includeammonia (NH₃). Particularly, when very pure nitrogen such as vaporizedfrom liquid nitrogen is used, unnecessary atoms are not introduced intothe nitride film resulting in few pinholes, little damage to dielectricproperty and small dispersion in dielectric strength.

The quality of insulating films can be furthermore improved by using ahalogen which would terminate dangling bonds and neutralize alkali ionsinadvertently introduced into the films. In this case, a halogencompound gas is introduced together with the process gas into thesputtering apparatus at 0.2 to 20 vol %. The halogen compound gasesinclude fluorine compounds such as NF₃, N₂ F₄, HF, chloro-fluoro carbonand F₂ and chlorine compounds such as CC₄, Cl₂ and HCl. If the halogenis introduced too much, the content of the insulating film might bealtered. The concentration of the halogen are limited to 0.01 to 5 atom% in general.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe invention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1(A) is a side view showing a MIS (metal-insulator-semiconductor)device manufactured in accordance with a first embodiment of the presentinvention.

FIG. 1(B) is a graphical diagram for explaining the displacement of theflat band voltage.

FIG. 2 is a graphical diagram showing the displacement of the flat bandvoltage versus the argon proportion to an argon and O₂ mixture in thesputtering atmosphere.

FIGS. 3(A) and 3(B) are side views showing a capacitance manufactured inaccordance with a second embodiment of the present invention.

FIG. 4 is a graphical diagram showing the dielectric strength versus theargon proportion in the sputtering atmosphere.

FIG. 5 is a graphical diagram showing the relative dielectric constantversus the argon proportion in the sputtering atmosphere.

FIG. 6 is a cross sectional view showing a DRAM provided with acapacitance manufactured in accordance with the first or secondembodiment of the present invention.

FIG. 7 is a cross sectional view showing another example of DRAMprovided with a capacitance manufactured in accordance with the first orsecond embodiment of the present invention.

FIG. 8 is a graphical diagram showing the displacement of the flat bandvoltage versus the argon proportion to an argon and N₂ mixture in thesputtering atmosphere.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1(A) and 1(B) and FIG. 2, a method ofmanufacturing an insulating film in accordance with a first embodimentof the present invention will be explained. A substrate 1 made of asingle crystalline silicon semiconductor is disposed on a substrateholder in an RF magnetron sputtering apparatus (not shown) in which atarget of Ta₂ O₅ has been mounted on a target holder in advance. Afterevacuating the inside of the apparatus, a gas is introduced thereinto inorder to prepare a suitable atmosphere for gas discharge. The gascomprises argon and an oxidizing gaseous compound such as oxygen.Desirably, the constituent gases have 99.999% or higher purities. Atantalum oxide film 3 (insulating film) is then sputtered on thesubstrate 1 by causing gas discharge between the target holder and thesubstrate holder. After completion of deposition, the substrate 1 isremoved from the apparatus and coated with a round aluminum electrode 4having a 1 mm diameter by electron beam evaporation.

The characteristics of such insulating film in the MIS structure(Al--Ta₂ O₅ --Si) can be evaluated by displacement ΔV_(FB) of the flatband voltage through measuring the flat band voltage. For themeasurement of the displacement, the insulating film is given BT(bias-temperature) treatment with a negative bias voltage of 2×10⁶ V/cmat 150° C. for 30 minutes followed by measuring the flat band voltageV_(FB1), and thereafter BT treatment with a positive bias voltage of2×10⁶ V/cm at 150° C. for 30 minutes followed by measuring the flat bandvoltage V_(FB2) again. The displacement ΔV_(FB) is |V_(FB1) -V_(FB2) |as illustrated in FIG. 1(B).

The above procedure of deposition was repeated by changing theproportion of argon to oxygen from 100% to 0% for reference. Thedisplacements ΔV_(FB) measured are plotted on a graphical diagram shownin FIG. 2. As shown in the diagram, the displacements ΔV_(FB)significantly decreased below 5 V when the argon proportion wasdecreased to 25% or lower. When argon was not used, i.e. pure oxygen(100%) was used, the displacements ΔV_(FB) was only 0.5 V or lower.Contrary to this, when pure argon (100%) was used, the displacementsΔV_(FB) was increased to 10 V. The displacements ΔV_(FB) was furthermoreabruptly decreased to several tenths thereof by utilizing an additive ofa halogen. The introduction of a halogen is carried out by introducinginto the sputtering apparatus, together with oxygen, a halogen compoundgas such as a nitrogen fluoride (NF₃, N₂ F₄) at 0.2 to 20 vol %.Particularly, NF₃ is most preferred because NF₃ can be handled with alittle care and decomposed by small energy.

Referring next to FIG. 3, a method of manufacturing an insulating filmin accordance with a second embodiment of the present invention will beexplained. A substrate 1 comprising a sodalime glass plate and a SiO₂blocking film formed thereon is disposed in a sputtering apparatus inwhich a target of metal tantalum has been set up in advance. Afterevacuating the inside of the apparatus, a gas is introduced thereintofor gas discharge. The gas comprises argon. A tantalum film 2 in theform of an island (lower electrode) is sputtered on the substrate to athickness of 2000 Å on the substrate 1 with the aid of a metallic maskby causing gas discharge between the target holder and the substrateholder. Alternatively, a known photolithography may be utilized insteadof the use of the metallic mask. The substrate temperature is 350° C.The pressure of the gas is maintained at 0.06 Torr during deposition.The input Rf energy is 100 W at 13.56 MHz.

After completion of deposition of the lower electrode 2, the gas isreplaced by a mixture of oxygen (100 vol % to 0 vol %) and argon (0 vol% to 100 vol %). The Ta target is also replaced by a Ta₂ O₅ targethaving a 99.99% or higher purity. A tantalum oxide film 3 (insulatingfilm) is then deposited on the lower electrode 2 by sputteringassociated with gas discharge between the target holder and thesubstrate holder. The substrate temperature is 100° C. The pressure ofthe gas is maintained at 0.05 Torr during deposition. The input Rfenergy is 500 W at 13.56 MHz. The distance between the substrate 1 andthe target is adjusted to be 150 mm. After completion of deposition, thesubstrate 1 is removed from the apparatus and coated with aroundaluminum film 4 (upper electrode) having a 1 mm diameter by electronbeam evaporation in order to form a capacitance comprising the lower andupper electrodes 2 and 4 and the interposed insulating (dielectric) film3.

The characteristics of such a capacitance were also evaluated bymeasuring the displacement ΔV_(FB) of the flat band voltage. When 100%oxygen was used, a very excellent capacitance was formed. Even if argonwas used up to 25%, capapitances having equivalent qualities were formedby setting the distance between the substrate 1 and the target to belarger than the appropriate value for the case of deposition using pureoxygen. Accordingly, excellent capacitances can be formed by utilizing amixture of oxygen (100 vol % to 25 vol %) and argon (0 vol % to 75 vol%). The quality of such insulating films can be furthermore improved byintroducing a halogen in the same manner as explained in conjunctionwith the first embodiment. In this case, the introduced halogen atomscan be activated by flash annealing using excimer laser pulses so thatdangling bonds occurring in the film are neutralized by the halogenatoms and the origin of fixed charge in the film is eliminated.

FIG. 4 is a graphical diagram showing the relationship between thedielectric strength of the film 3 and the oxygen proportion to theargon-oxygen mixture. The dielectric strength is measured as thethreshold voltage when the current leakage exceeds 1 μA. In thisdiagram, the length of vertical lines corresponds to double the standarddeviations σ(X) and given center dots indicative of averagesrespectively. As shown in the diagram, the σ(X) decreased and theaverage dielectric strengths increased as the proportion increasedbeyond 75%. FIG. 5 is a graphical diagram showing the relationshipbetween the relative dielectric constant of the film 3 and the oxygenproportion to the argon-oxygen mixture in the same manner. In thisdiagram, it is also understood that high proportions of oxygen areadvantageous resulting in small dispersions.

Referring next to FIG. 6, a suitable application of the insulating filmformed in accordance with the first or second embodiment of the presentinvention will be explained. The insulating film is used to form storagecapacitances coupled with gate insulated field effect transistors forconstructing a DRAM (dynamic random access memory) of 1 Tr/Cell type.

A storage element of the DRAM is of a stacked type as illustrated inFIG. 6 and comprises an n-type silicon semiconductor substrate withinwhich a source and drain regions 8 and 9 of p-type are formed in orderto define a channel region therebetween, a field insulating film 5(LOCOS) for insulating the element from adjacent elements, a gateelectrode 7 formed on the channel region through a gate insulating film6 formed by thermal oxidation or sputtering of silicon oxide in 100%oxygen, an interlayer insulation film 14, a lower electrode 10 made of asilicon semiconductor heavily doped with phosphorus, a dielectric(insulating) film 11 and an upper electrode 12 formed of an aluminumfilm or a dual film comprising an aluminum layer and a tantalum layer.

The lower electrode 10 may be formed of metal tantalum, tungsten,titanium, molybdenum or any of silicides of such metals and makeselectric contact with the drain region 9 through an opening formed inthe interlayer film 14. The dielectric film 11 is formed of a Ta₂ O₅film deposited by sputtering to a thickness of 300 Å to 3000 Å,typically 500 Å to 1500 Å, e.g. 1000 Å in accordance with the first orsecond embodiment as described above. The gate insulating film 6 can bemade also from Ta₂ O₅ in place of silicon oxide. In that case, thenumber of interface states is as small as 2×10¹⁰ cm⁻². A storagecapacitance is formed of the upper and lower electrodes 10 and 12 andthe dielectric film 11 located therebetween. The formation of trappingcenters of hot carriers can be avoided by forming these electrodes 10and 12 and the dielectric film 11 in an atmosphere which has beendeprived of hydrogen, which otherwise could reach to the gate insulatingfilm by drifting (diffusion). The channel length of the element isselected between 0.1 μm and 1.0 μm, e.g. 0.5 μm so that one storageelement can be formed within an area of 20 μm square. The source region8 is connected to a bit line for example, and in that case the gateelectrode 7 is connected to an address line of the memory. Suchminiaturized structure becomes possible due to the large storagecapacitance originating from the large relative dielectric constant(=27) of the tantalum oxide film as compared to the relative dielectricconstant (=3.8) of silicon oxide. The large relative dielectric constantmakes it possible to increase the thickness of the dielectric film to,e.g. 1000 Å so that electric insulation is improved and the number ofpinholes is decreased. The frequency property of the tantalum oxide filmis also excellent and maintained even at high frequencies. In thefigure, numeral 12' designates an extension of the upper electrode of anadjacent storage element. Numeral 13 is the bit line of an adjacentelement.

Referring next to FIG. 7, another application of the insulating filmformed in accordance with the first or second embodiment of the presentinvention will be explained. The insulating film is used to form storagecapacitances for a DRAM (dynamic random access memory) of 1 Tr/Celltype.

A storage unit element of the DRAM illustrated in FIG. 7 can storeinformation of two bits. The element comprises a p-type siliconsemiconductor substrate within which a pair of channel regions 15 and15' of n-type and a pair of drain regions 8 and 8' of p-type are formed,a plateau of a p-type semiconductor material forming a source region 9located between the channel regions 15 and 15', a source electrode 19formed on the plateau, a pair of gate electrodes 7 and 7' formed on thechannel regions 15 and 15' through a gate insulating film 6 and flankingthe side surface of the source region 9, a field insulating film 5(LOCOS) for insulating the element from adjacent elements, an interlayerinsulation film 14, a pair of lower electrodes 10 and 10' made ofsilicon semiconductor heavily doped with phosphorus, a dielectric(insulating) film 11 and a pair of upper electrodes 12 and 12' formed ofan aluminum film or a dual film comprising an aluminum layer and atantalum layer. The channel region 15 and 15' are formed by ionimplantation of boron with a masks of the plateau 9 and 19 and the fieldinsulating film 5 to a density of 1×10¹⁵ cm⁻³ to 5×10¹⁶ cm⁻³, in advanceof the formation of the gate electrodes 7 and 7', followed by ionimplantation of phosphorus into the regions 8 and 8' with a mask of theplateau 9 and 19, the field insulating film 5 and the gate electrodes 7and 7' to a density of 1×10¹⁹ cm⁻³ to 1×10²¹ cm⁻³.

The lower electrodes 10 and 10' make electric contact with the drainregions 8' and 8 through openings formed in the interlayer film 14respectively. The dielectric film 11 is formed of a Ta₂ O₅ filmdeposited by sputtering to a thickness of 300 Å to 3000 Å, typically 500Å to 1500 Å, e.g. 1000 Å in accordance with the first or secondembodiment as described above in the same manner as that of the previousapplication. The lower electrode may be formed of metal tantalum,tungsten, titanium, molybdenum or any of silicides of these metals inplace of the doped silicon semiconductor. A pair of storage capacitances21 and 21' are formed from the upper and lower electrodes 10, 10' and12, 12' and the dielectric film 11 therebetween. The channel length ofthe element is selected between 0.1 μm and 1.0 μm, e.g. 0.5 μm so that atwo bit storage element can be formed within an area of 10 to 20 μmsquare.

Next, a method of manufacturing an insulating film in accordance with athird embodiment of the present invention will be explained. FIG. 1(A)is used again for this purpose. A substrate 1 made of a singlecrystalline silicon semiconductor is disposed on a substrate holder inan RF magnetron sputtering apparatus (not shown) in which a target ofSi₃ N₄ has been mounted on a target holder in advance. Alternatively,the target may be made of other nitrides such as aluminum nitride,tantalum nitride, titanium nitride instead of the Si₃ N₄ target. Afterevacuating the inside of the apparatus, a gas is introduced thereinto inorder to prepare a suitable atmosphere for gas discharge. The gascomprises argon and a nitrogen compound gas such as nitrogen. Desirably,the constituent gases have 99.9% or higher purities. The substratetemperature is 200° C. The pressure of the gas is maintained at 0.05Torr during deposition. The input Rf energy is 500 W at 13.56 MHz. Thedistance between the substrate 1 and the target is adjusted to be 150mm. A silicon nitride film 3 (insulating film) is then sputtered on thesubstrate 1 by causing gas discharge between the target holder and thesubstrate holder. After completion of deposition, the substrate 1 isremoved from the apparatus and coated with a round aluminum electrode 4having a 1 mm diameter by electron beam evaporation.

The characteristics of such insulating film in the MIS structure(Al--Si₃ N₄ --Si) can be evaluated by displacement ΔV_(FB) of the flatband voltage through measuring the flat band voltage. For themeasurement of the displacement, the insulating film is given BT(bias-temperature) treatment with a negative bias voltage of 2×10⁶ V/cmat 150° C. for 30 minutes followed by measuring the flat band voltage,and thereafter BT treatment with a positive bias voltage of 2×10⁶ V/cmat 150° C. for 30 minutes followed by measuring the flat band voltageagain in the same manner as for oxide films.

The above procedure of deposition was repeated by changing theproportion of argon to nitrogen from 100% to 0% for reference. Thedisplacements ΔV_(FB) measured are plotted on a graphical diagram shownin FIG. 8. As shown in the diagram, the displacements ΔV_(FB)significantly decreased below 2 V when the argon proportion wasdecreased to 25% or lower. Numeral 31 designates a displacement of 11.5V in the case of a silicon nitride film deposited by a conventionalplasma CVD for reference. When argon was not used, i.e. pure nitrogen(100%) was used, the displacements ΔV_(FB) was only 0.5 V or lower asdepicted by numeral 34. Contrary to this, when pure argon (100%) wasused, the displacements ΔV_(FB) was increased to 13 V. The displacementsΔV_(FB) was furthermore abruptly decreased to several tenths thereof byutilizing an additive of a halogen. The introduction of a halogen iscarried out by introducing into the sputtering apparatus, together withnitrogen, a halogen compound gas such as a nitrogen fluoride (NF₃, N₂F₄) at 0.2 to 20 vol %. In this case, the introduced halogen atoms canbe activated by flash annealing using excimer laser pulses so thatdangling bonds occurring in the film are neutralized by the halogenatoms and the origin of fixed charge in the film is eliminated.

Referring again to FIGS. 6 and 7, suitable applications of theinsulating film formed in accordance with the third embodiment of thepresent invention will be explained. The insulating film is used also inthis case to form storage capacitances for DRAMs (dynamic random accessmemory) of 1 Tr/Cell type. The explanation is substantially same asgiven to the above applications utilizing the tantalum oxide insulatingfilms except for the following description.

The dielectric film 11 as illustrated in FIGS. 6 and 7 is formed of aSi₃ N₄ film in this case deposited by sputtering to a thickness of 300 Åto 3000 Å, typically 500 Å to 1500 Å, e.g. 1000 Å in accordance with thethird embodiment as described above. The gate insulating film 6 can bemade also from Si₃ N₄ in place of silicon oxide. In that case, thenumber of interface states is as small as 3×10¹⁰ cm⁻². The dimension ofthe unit elements can be decreased in the same manner as in theapplications utilizing the tantalum oxide films due to the large storagecapacitance originating from the large relative dielectric constant (=6)of the silicon nitride film as compared to the relative dielectricconstant (=3.8) of silicon oxide.

The foregoing description of preferred embodiments has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form described, andobviously many modifications and variations are possible in light of theabove teaching. The embodiment was chosen in order to explain mostclearly the principles of the invention and its practical applicationthereby to enable others in the art to utilize most effectively theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated.

Although the dielectric films are deposited by RF magnetron sputteringin the above preferred embodiments, other suitable sputtering can beutilized, e.g. various known types of DC or RF sputtering methods. It ispartly because of the high resistance of the targets utilized that RFmagnetron sputtering is preferred. Pure metals such as tantalum andtitanium, however, may be used in suitable sputtering conditions. In thecase of deposition of oxide films by the use of such targets of puremetals, the atmosphere is purified to a 99.999% or higher purity andcomprises 100% to 90% oxygen in which deposition of the oxide films iscarried out with a lower acceleration voltage at a lower depositionspeed of the order of 1/4 of the above embodiments.

The application of the present invention is not limited to the aboveexamples but applicable for integrated circuits utilizing the capacitorsof the present invention, transistors of inversed-stagger type, verticalchannel transistors, other types of insulated gate field effecttransistors formed within a single crystalline silicon semiconductorsubstrate and so forth. The capacitances can be formed intomulti-layered structure or vertical type structure in which thedielectric film is sandwiched by a pair of electrodes in a lateraldirection. The capacitors of the present invention can be used fordynamic memories.

What is claimed is:
 1. A method of forming an oxide dielectric layer ofa storage capacitor coupled with a transistor for a DRAM (dynamic randomaccess memory), said method comprising the steps of:preparing asemiconductor substrate having at least source, drain and channelregions of said transistor formed therein; forming a lower electrode ofsaid storage capacitor on said semiconductor substrate, said lowerelectrode being connected to one of said source or drain of saidtransistor; forming said oxide dielectric layer on said lower electrodeby sputtering in a sputtering gas, said oxide dielectric layercomprising an oxide of a metal; and forming an upper electrode of saidcapacitor on said dielectric layer, wherein said sputtering gas containsan oxygen containing gas at a concentration of 75% or higher.
 2. Themethod of claim 1 wherein said metal is selected from the groupconsisting of tantalum and titanium.
 3. The method of claim 2 whereinsaid oxygen containing gas is selected from the group consisting of O₂,O₃, and N₂ O.
 4. A method of forming an oxide dielectric layer of astorage capacitor coupled with a transistor for a DRAM, said methodcomprising the steps of:preparing a semiconductor substrate having atleast source, drain and channel regions of said transistor formedtherein; forming a lower electrode of said storage capacitor on saidsemiconductor substrate, said lower electrode being connected to one ofsaid source or drain of said transistor; forming said oxide dielectriclayer on said lower electrode by sputtering in a sputtering gas, saidoxide dielectric layer comprising a ferroelectric material, and formingan upper electrode of said capacitor on said dielectric layer whereinsaid sputtering gas contains an oxygen containing gas at a concentrationof 75% or higher.
 5. The method of claim 4 wherein said oxygencontaining gas is selected from the group consisting of O₂, O₃, and N₂O.
 6. The method of claim 5 wherein said ferroelectric material isselected from the group consisting of barium titanate and lead titanate.7. A method of forming an oxide dielectric layer of a storage capacitorcoupled with a transistor for a DRAM, said method comprising the stepsof:preparing a semiconductor substrate having at least source, drain andchannel regions of said transistor formed therein; forming a LOCOS(field insulating film) on or within said semiconductor substrate forisolating said transistor; forming a lower electrode of said storagecapacitor on said semiconductor substrate, said lower electrode beingconnected to one of said source or drain of said transistor; formingsaid oxide dielectric layer on said lower electrode by sputtering in asputtering gas, said oxide dielectric layer comprising a ferroelectricmaterial, and forming an upper electrode of said capacitor on saiddielectric layer, wherein said capacitor is located over at least aportion of said LOCOS, wherein said sputtering gas contains an oxygencontaining gas at a concentration of 75% or higher.
 8. The method ofclaim 7 wherein said oxygen containing gas is selected from the groupconsisting of O₂, O₃, and N₂ O.
 9. The method of claim 7 wherein saidferroelectric material is selected from the group consisting of bariumtitanate and lead titanate.
 10. A method of forming an oxide dielectriclayer of a storage capacitor coupled with a transistor for a DRAM, saidmethod comprising the steps of:preparing a semiconductor substratehaving at least source, drain and channel regions of said transistorformed therein; forming a lower electrode of said storage capacitor onsaid semiconductor substrate, said lower electrode being connected toone of said source or drain of said transistor; forming said oxidedielectric layer on said lower electrode by sputtering in a sputteringgas, said oxide dielectric layer comprising a ferroelectric material;and forming an upper electrode of said capacitor on said dielectriclayer, wherein said sputtering gas contains an oxygen containing oxygenat a concentration of 75% or higher, wherein said capacitor is locatedover at least a portion of a gate electrode of said transistor.
 11. Themethod of claim 10 wherein said ferroelectric material is selected fromthe group consisting of barium titanate and lead titanate.
 12. Themethod of claim 10 wherein said DRAM is of a 1 Tr/Cell type.
 13. Amethod of forming a nitride dielectric layer of a storage capacitorcoupled with a transistor for a DRAM, said method comprising the stepsof:preparing a semiconductor substrate having at least source, drain andchannel regions of said transistor formed therein; forming a lowerelectrode of said storage capacitor on said semiconductor substrate,said lower electrode being connected to one of said source or drain ofsaid transistor; forming said nitride dielectric layer on said lowerelectrode by sputtering in a sputtering gas, said oxide dielectric layercomprising a nitride, and forming an upper electrode of said capacitoron said dielectric layer, wherein said sputtering gas contains nitrogenat a concentration of 75% or higher.